Device for intensifying photoelectrostatic image



July 5, 1955 c. ORLANDO 2,712,607

DEVICE FOR INTENSIFYING PHOTOELECTROSTATIC IMAGE Filed July 1, 1952 CARLORLANDO ww @SLM nited States Patent DEVICE FOR INTENSIFYINGPHOTOELECTRO- STATIC IMAGE Carl Orlando, Long Branch, N. J., assigner tothe United States of America as represented by the Secretary of the ArmyApplication July 1, 1952, Serial No. 296,780 S Claims. (Cl. 250-49.5)(Granted under Title 35, U. S. Code (1952), sec. 266) The inventiondescribed herein may be manufactured and used by and for the Governmentfor governmental purposes without payment of any royalty thereon.

This invention relates to electrophotography and more particularly to adevice and method for intensifying a photoelectrostatic image.

lt is an object of the present invention to provide a u device fortransferring a photoelectrostatic image from one surface to a secondsurface resulting in an overall increase in the latent intensity of saidimage on the second surface.

It is a further object to provide a method for increasing the latentintensity of a photoelectrostatic image.

In accordance with the present invention, there is provided a device forintensifying a photoelectrostatic image comprising an evacuable chamber,an electron emissive source at one end of the chamber and an electroncollecting plate on the other end thereof. Means are provided foraccelerating and focusing the emitted electrons from the electron sourceto the electron collecting plate. Means for controlling the flow ofelectrons between the electron source and the electron collecting platecomprising a negatively charged screen having a photoelectrostatic imagethereon is interposed between the electron source and the acceleratingand focusing means. Removable means is provided for permitting egress toand ingress from the chamber and means is also provided for evacuatingthe chamber.

Also, in accordance with the present invention, there is provided amethod for intensifying a photoelectrostatic image comprising negativelycharging a screen of small mesh coated on one side with a photosensitivematerial and exposing the negatively charged photosensitive coating onsaid screen to alight image to form a photoelectrostatic image thereon.The exposed screen is then inserted into an evacuable chamber whichcontains an emissive source of electrons on one end thereof, means forcollecting electrons at the other end thereof, and means intermediatethe electron source and the electron collecting means for acceleratingand focusing the electrons from the electron source. The exposed screenis inserted into the chamber intermediate the accelerating and focusingmeans and the electron emissive source. The chamber is evacuated and theelectron source and the electron collecting means are electricallyconnected whereby electrons are emitted from the electron source and areaccelerated and impinge on the electron collecting means. The electronow is controlled by the negatively charged screen and the electrons arefocused onto the electron collecting means by the electron acceleratingand focusing means. The electron collecting means is thereafter removedfrom the chamber and the latent photoelectrostatic image which has beentransferred from the negatively charged screen to the electroncollecting means in an intensified form, is developed.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection 2371-2351)? Patented July 5, 1955 withthe accompanying drawing and its scope will be pointed out in theappended claims.

Referring to the drawing, there is shown a device for intensifying aphotoelectrostatic image in accordance with the invention comprising anevacuable chamber of suitable opaque material 1 having an electronemissive source 2 at one end thereof, said source being a screen cathodeof small mesh equal to or greater than 500 mesh per inch and comprisinga substance which readily emits electrons under vacuum conditions and atmoderately warm temperatures. The emitting qualities do not necessarilyhave to be equal to those found in an electronic vacuum tube since thesystem described does not depend on time elements of the magnitudenecessary for vacuum tube applications. The electron source is arrangedto project a beam of electrons to an electron collecting means 3 locatedat the other end of chamber 1 and comprises a plate consisting of aconductive material coated on one side with a non-conductive substanceil capable of accepting and retaining an electrostatic charge. Thisplate is used to obtain the nal photograph of thetransferredphotoelectrostatic image. interposed between screen cathode 2and electron collecting means 3 is a photosensitive screen 4 of smallmesh comprising a screen of conductive material coated on one side witha light sensitive substance 12 such as selenium or other suitablematerial. The screening of photosensitive screen 4 is of the order of anamount equal to or greater than 500 mesh per inch. This high number ofmesh is required since the resolution of the nal photograph is in directrelation to the number of openings present in the screen. lntermediatephotosensitive screen 4 and electron collecting plate 3, there isprovided a focusing and accelerating screen electrode 5 comprising aconductive material having a mesh substantially equal to that ofphotosensitive screen 4. Said focusing electrode 5 is maintained at apositive potential with respect to cathode 2 by means of battery 6 orany other suitable source. Removable means illustrated at 7 for egressand ingress are provided in evacuable chamber 1 and means for evacuatingthe chamber t0 the required degree is provided as indicated at 8.

Considering the operation of this device in obtaining a finalphotograph, light sensitive coating l2 on photosensitive screen 4 ischarged negatively and is exposed to a light image. Coating 12 isexposed to the light image in a camera or other suitable photographicdevice. lt is then placed in chamber 1 intermediate electron source 2and focusing screen 5 and chamber 1 is then evacuated. Removal of thephotosensitive screen 4 with the light image impressed on lightsensitive coating i2 from the photographic device does not disturb thecharge on coating 12 since this charge is electrostatic and is thusretained on coating 12 for an appreciable period. This period is quitesufficient to permit the transferral of screen 4 from a photographicdevice to chamber 1. Light sensitive coating 12 need not be in the formof a photographic emulsion but is preferably in the form of a coating oflight sensitive material such as selenium. All elements in chamber 1 areconnected electrically by battery 6. The photosensitive screen 4 isnegative with respect to electron source 2; the focusing screen 5 ispositive to the electron source 2; and electron collecting plate 3 ispositive with respect to focusing screen S. The electrical action iscarried on for a predetermined time after which the electron collectingplate 3 is removed and a charged charcoal powder or similar substance isimpressed on its surface to enable the electron image on the electroncollecting plate 3 to be developed to a visible image. Non-conductivesubstance 11, in the same manner as light sensitive coating 12, lirmlyretains the electrostatic charge impressed thereon for an appreciableperiod permitting the removal of electron collecting means 3 fromchamber 1 for development within a reasonable period.

To form an original photoelectrostatic image, light is impressed uponthe non-exposed negatively charged photosensitive screen 4, thus causinga decrease in the number of electrostatic charges on the individual par#ticles of said screen which is proportional to the quantum of lightfalling upon the individual light sensitive particles comprising thescreen.

After exposing photosensitive screen 4 to a light image, it is placedwithin chamber 1 which is then evacuated. Electron emissive source 2 isactivated to produce a cloud of electrons within the chamber. Theelectron cloud emitted is attracted to the positive electrodes inchamber 1; namely the focusing screen 5 and the electron collectingplate 3. Photosensitive screen 4, since it is negatively charged, willretard the passage of electrons. The amount of retardation isproportional to the number of electrostatic charges present on thephotosensitive screen. This action is similar to the action of a controlgrid in a triode type vacuum tube. Electrons which have passed throughthe openings of the meshed photosensitive screen 4 are accelerated anddirected by the focusing screen 5 so that they impinge on collectingplate 3. Stray electrons will be collected by focusing screen 5 whileelectrons traveling parallel to photosensitive screen 4 and focusingscreen S mesh openings will not be collected by said focusing screen andwill pass therethrough to irnpinge on electron collecting plate 3.Discrete sections of plate 3 will be charged negatively; the amount ofcharge being proportional to (l) the amount of electrons impingingthereon, (2) the length of time the electrical action takes place, (3)the electron cloud density, and (4) the charge present on exposedphotosensitive screen 4. Thus, within a given time and given electroncloud density, there will be a charge impressed on any given point onelectron collecting plate 3 which is proportional to a correspondingpoint on photosensitive screen 4. Since the charges on saidphotosensitive screen have a great influence on the number of electronsthat can pass through its screen openings after a predetermined periodof time has elapsed, the amount of charges impressed between any twopoints on'electron collecting plate 3 is greater than the correspondingcharge on photosensitive screen 4.

In effect, what has been accomplished is the impressing of a greaterelectrostatic charge on the electron collecting plate resulting in astronger electrostatic image corresponding to the relatively weak imageon the negatively charged photosensitive screen. The electron collectingplate acquires a latent photoelectrostatic image negative While therehas been described what is at present considered to be the preferredembodiment of this invention,

lli

it will be obvious to those skilled in the art that various changes andmodications may be made therein without departing from the invention,and it is, therefore, aimed in the appended claims to cover all suchchanges and modificationsV as fall within the true spirit and scope ofthe invention.

What is claimed is:

1. A device for intensifying a photoelectrostatic image comprising anevacuable chamber, an emissive electron source within said chamber atone end thereof, electron collecting means at the. other end thereof,means for focusing said emitted electrons to impinge on said collectingmeans, means intermediate said electron source and said focusing meansfor controlling the amount of electrons impinging on said collectingmeans comprising a screen having a photoelectrostatic image thereon,removable means for permitting ingress to and egress from said chamber,and means for evacuating said chamber.

2. A device for intensifying a photoelectrostatic image as in claim lwherein said electron source is a screen cathode of small mesh adaptedto emit electrons under vacuum conditions at moderately warmtemperatures.

3. A device Vfor intensifying a photoelectrostatic image as in claim 1wherein said electron collecting means comprises a conducting platecoated on one side with a nonconductive material for retaining anelectrostatic charge.

4. A device for intensifying a photoelectrostatic image as in claim 1wherein said controlling means comprises a negatively charged conductingscreen of small mesh, a photosensitive coating on one side, saidphotosensitive coating having a photoelectrostatic image thereon.

5. A device for intensifying a photoelectrostatic image as in claim lwherein said focusing means comprises a screen of small mesh.

References Cited in the le of this patent i UNITED STATES PATENTS

